"We have a serious risk of having a big cholera epidemic in this part of the world ... We have a population that is on the move, an unstable security situation and a population that does not have access to safe water and proper sanitation," she told Al Jazeera from Geneva.

Chaigot said that fresh fighting would further hinder efforts to get aid and medical supplies to people already hard to reach.

Our correspondent found desperate refugees surviving on leaves and hundreds of others trying to return to their homes - a movement that could lead to further cholera outbreaks, health workers say.

The humanitarian crisis exploded after rebel leader Laurent Nkunda launched an offensive on August 28, stopping his forces at the gates of Goma before declaring a ceasefire.

Retreating Congolese troops and rebels sent the population fleeing and sporadic clashes have broken out since then despite the ceasefire.

Thousands of refugees are packed into camps or sleeping out in the open and Weekend clashes between rebels and soldiers increased fears that patients could scatter and start an epidemic.

Vow to repel outsiders

A summit of southern African leaders said on Sunday that members could, if necessary, send peacekeepers to bolster UN peacekeepers.

The United Nations has a 17,000-strong peacekeeping force in DR Congo, and is asking for an extra 3,000 troops as the current force is thinly stretched across the country the size of western Europe.

"If they come in and fight ... I am ready to fight them. They will share the same shame as the DRC government"

Laurent Nkunda, leader of the National Congress for the Defence of the People

But it appears unlikely that a European Union force will move to help the UN stem the fighting.

France failed to secure support from other European Union nations on Monday for sending a 1,500-strong EU battlegroup to eastern Congo to bolster the UN force.

Nkunda has said he will fight any troops sent to support the DR Congo army.

"If they come in and fight alongside the FARDC [DR Congo army] and the FDLR [pro-government Hutu fighters], they will be weakened," Nkunda told the Reuters news agency by telephone from eastern Congo.

"I am ready to fight them. They will share the same shame as the DRC government."

Southern African leaders also renewed calls for a ceasefire and the creation of humanitarian corridor.

But Nkunda said his forces were upholding a fragile ceasefire and called on the government to enter into negotiations.

"We declared the ceasefire, and we're still sticking to it," he said.

More than 250,000 people have fled their homes to escape the fighting between government forces and Nkunda's National Congress for the Defence of the People in recent weeks.